Generally, the widely-used peripheral input device of a computer system includes for example a mouse device, a keyboard device, a trackball device, or the like. Via the keyboard device, characters or symbols can be directly inputted into the computer system. As a consequence, most users and most manufacturers of input devices pay much attention to the development of keyboard devices. For example, a keyboard device with plural key structures is one of the common keyboard devices.
Hereinafter, a key structure of a keyboard device is shown. The key structure comprises a scissors-type connecting element. FIG. 1 is a schematic cross-sectional side view illustrating a conventional key structure. As shown in FIG. 1, the conventional key structure 1 comprises a keycap 11, a scissors-type connecting element 12, a rubbery elastomer 13, a membrane switch circuit member 14 and a base plate 15. The keycap 11, the scissors-type connecting element 12, the rubbery elastomer 13 and the membrane switch circuit member 14 are supported by the base plate 15. The scissors-type connecting element 12 is used for connecting the base plate 15 and the keycap 11.
The scissors-type connecting element 12 is arranged between the base plate 15 and the keycap 11, and the base plate 15 and the keycap 11 are connected with each other through the scissors-type connecting element 12. The scissors-type connecting element 12 comprises a first frame 121 and a second frame 122. A first end of the first frame 121 is connected with the keycap 11. A second end of the first frame 121 is connected with the base plate 15. The rubbery elastomer 13 is enclosed by the scissors-type connecting element 12. The membrane switch circuit member 14 comprises plural key intersections (not shown). When one of the plural key intersections is triggered, a corresponding key signal is generated. The rubbery elastomer 13 is disposed on the membrane switch circuit member 14. Each rubbery elastomer 13 is aligned with a corresponding key intersection. When the rubbery elastomer 13 is depressed, the rubbery elastomer 13 is subjected to deformation to push the corresponding key intersection of the membrane switch circuit member 14. Consequently, the corresponding key signal is generated.
The operations of the conventional key structure 1 in response to the depressing action of the user will be illustrated as follows. Please refer to FIG. 1 again. When the keycap 11 is depressed, the keycap 11 is moved downwardly to push the scissors-type connecting element 12 in response to the depressing force. As the keycap 11 is moved downwardly relative to the base plate 15, the keycap 11 pushes the corresponding rubbery elastomer 13. At the same time, the rubbery elastomer 13 is subjected to deformation to push the membrane switch circuit member 14 and trigger the corresponding key intersection of the membrane switch circuit member 14. Consequently, the membrane switch circuit member 14 generates a corresponding key signal. When the keycap 11 is no longer depressed by the user, no external force is applied to the keycap 11 and the rubbery elastomer 13 is no longer pushed by the keycap 11. In response to the elasticity of the rubbery elastomer 13, the rubbery elastomer 13 is restored to its original shape to provide an upward elastic restoring force. Consequently, the keycap 11 is returned to its original position where it is not depressed. The structures and the operations of the conventional key structure have been mentioned as above.
With increasing development of science and technology, the functionality and slimness benefit of the keyboard device are gradually enhanced and thus the demands of the user on the keyboard device are gradually increased. For example, the user prefers that the thickness of the keyboard device is reduced and the movement of the key structure is more stable when the key structure is depressed. For achieving the above purpose, a keyboard device with a butterfly-type connecting element has been introduced into the market and disclosed in U.S. Pat. No. 6,586,695. The keyboard device as disclosed in U.S. Pat. No. 6,586,695 comprises a keycap, a butterfly-type connecting element and a fixing element. The butterfly-type connecting element comprises a first frame and a second frame. The first frame is located beside a first side of the keycap and connected with a middle region of the keycap and the fixing element. The second frame is located beside a second side of the keycap and connected with the middle region of the keycap and the fixing element. While the keycap is depressed, the keycap is moved downwardly to push the butterfly-type connecting element. Consequently, the first frame and the second frame are swung and slid relative to the fixing element, and the function of depressing the key structure is achieved.
In the butterfly-type connecting element, the first frame and the second frame are located adjacent to each other. In comparison with the scissors-type connecting element, the displacement amount of the butterfly-type connecting element in the vertical direction is small. Consequently, the movement of the key structure is more stable when the key structure is depressed, and the keyboard device with the butterfly-type connecting element is thinner. However, since both of the first frame and the second frame are connected with the middle region of the keycap, some drawbacks occur. For example, when a corner of the keycap is depressed, the pressing force cannot be effectively transferred to the butterfly-type connecting element. Under this circumstance, it is difficult to depress the butterfly-type connecting element. In other words, the user has to accurately press the middle region of the keycap in order to smoothly depress the keycap.
Therefore, there is a need of providing a keyboard device for transferring the pressing force easily.